Method for recording data and device for carrying out the same comprising a deformable memory support

ABSTRACT

The recording device comprises a network of micro-points ( 6 ), with tips of nanometer scale, fixed to the same substrate ( 7 ). Said network of micro-points cooperates with a deformable memory support ( 1 ), which absorbs the range of differing heights of the micro-points ( 6 ) on bringing the network into contact with the memory support, before thermal, electrical, and/or mechanical recording of data. The memory support ( 1 ) comprises a stack with at least one deformable memory layer, arranged on a substrate ( 4 ). The deformable memory layer may be embodied by the stacking of a memory layer ( 2 ) and a flexible layer ( 3 ), the latter being arranged on the substrate ( 4 ). The memory layer ( 2 ) can be covered by a layer ( 5 ) interfacing with the micro-points ( 6 ). The pressure of a micro-point ( 6 ) on the memory support ( 1 ) induces a progressive deformation of the stack up to the flexible layer ( 3 ).

BACKGROUND OF THE INVENTION

The invention relates to a method for recording data by means of anarray of micro-tips arranged in a plane facing a memory support,comprising a stack of thin layers with at least one deformable memorylayer. This method comprises data recording by selective actuation ofthe micro-tips.

The invention also relates to a device for recording data forimplementation of the method for recording.

STATE OF THE ART

Data recording, both in the computing field and in the multimedia field,has to meet an increasing need for capacity. Different techniques havebeen developed ranging from the magnetic hard disk to the DVD usingoptics and phase change materials. Whatever the recording techniqueused, it is always sought to reduce the size of the memory points (bits)and increasing the recording capacity necessarily means increasing thestorage density.

Recently, very large storage capacities, of about a Terabit/cm², havebeen obtained by implementing micro-tips of the type used in the tipeffect microscopy field (“The Millipede—More than one thousand tips forfuture AFM data storage”, P. Vettiger et al., IBM J. RES. Develop., Vol.44, no 3, May 2000, p. 323-340 and “Fabrication of microprobe array withsub-100 nm nano-heater for nanometric thermal imaging and data storage”,Dong-Weon Lee et al., Technical Digest, MEMS 2001, 14^(th) IEEEInternational Conference on Micro Electro Mechanical Systems (Cat. No01CH37090), IEEE, Piscataway, N.J., USA, 2001, p. 204-207). High densityis obtained by localizing the bits by means of micro-tips having an apexof nanometric scale. The micro-tips are preferably arranged in atwo-dimensional array, with parallel access to the data, which enablesexcellent performances to be achieved as far as capacity is concerned. Asingle actuator, which may be electromechanical, enables a relativemonolithic movement of the whole micro-tip array with respect to thesurface of the storage medium constituting the memory support. Writingis then performed thermo-mechanically.

In such a data recording device, with tip effect, a perfect contact ofall the tips with the storage medium has to be guaranteed. For reasonsof complexity of the system, it can not be envisaged to control theposition of each micro-tip individually. The micro-tips are howeverfabricated in collective manner, by techniques derived from those ofmicroelectronics, and a dispersion of the height of the micro-tipsalways remains due to fabrication. Although this dispersion is verysmall, typically about 100 nm, the longest of the micro-tips of an arraypresses more than the others on the memory support.

To overcome this difficulty, each micro-tip is borne overhanging by oneend of a cantilever, in similar manner to the micro-tip arrays used inlocal probe microscopy. The flexibility of the cantilever then enablesthe strain of a bearing to be absorbed.

The documents WO-A-97/44780, EP-A-887794 and U.S. Pat. No. 6,218,086also describe recording devices wherein each micro-tip is arranged atthe end of a cantilever. Simply placing the micro-tip and the memorysupport in contact causes bending of the cantilever enabling theheightwise dispersion of the micro-tips to be partially compensated. Torecord an item of information, a local deformation of the memory supportis caused either thermally or mechanically.

However, the bearing forces of the micro-tips on the memory support mustnot exceed a value of about 100 nN for example, so as not to damage thememory support. Indeed, as the contact surface of a micro-tip with thestorage medium is minute, the pressure is high. The cantileverstherefore have to be very flexible to absorb the heightwise dispersionof the micro-tips. For example, cantilevers having a stiffness of about1 N/m, a length of 100 μm, a width of a few tens of micrometers and athickness of a few micrometers have been developed.

It is difficult to envisage more flexible cantilevers. Their dimensionsare in fact difficult to master due to their large length in comparisonwith their small width and/or thickness. In addition, the precision ofpositioning of the tips facing the surface of the memory support wouldbe adversely affected, thus limiting the memory density.

OBJECT OF THE INVENTION

The object of the invention is to achieve a method and a device for datarecording not presenting the above shortcomings and more particularlyenabling the heightwise dispersion of the micro-tips to be ignored.

According to the invention, this object is achieved by a method and adevice according to the accompanying claims.

A method for recording according to the invention is more particularlycharacterized by the fact that, the micro-tips being fixed directly ontoone and the same support substrate, the method comprises bringing thearray of micro-tips and the memory support into contact with apredetermined pressure, before selective actuation of micro-tips fordata recording, said pressure enabling the dispersion of the dimensionsof the micro-tips of the array of micro-tips to be absorbed by thedeformable memory layer.

A device for implementing the method according to the inventioncomprises an array of micro-tips arranged in a plane facing a memorysupport, comprising a stack of thin layers with at least one deformablememory layer, means for absorbing the dispersion of the dimensions ofthe micro-tips of the array and means for recording by selectiveactuation of the micro-tips. This device is characterized in that thedeformable memory layer constitutes said means for absorbing when thememory support and the micro-tip array are brought into contact, at saidpredetermined pressure, the micro-tips, with tips of nanometricdimension, being fixed directly onto one and the same support substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention givenas non-restrictive examples only and represented in the accompanyingdrawing, in which the single FIGURE schematically illustrates aparticular embodiment of a device for recording data according to theinvention.

DESCRIPTION OF A PARTICULAR EMBODIMENT

The array of micro-tips of a data recording device according to theinvention comprises a plurality of micro-tips 6 fixed directly, i.e.without cantilevers, to the same substrate 7. The micro-tips aretherefore securedly fixed to the substrate 7, which is preferably rigid.

Before selective actuation of the micro-tips for recording the data, thesupport substrate 7 of the micro-tips 6 is moved in the direction of thememory support 1 so as to bring simultaneously all the micro-tips 6 intocontact with the memory support 1 at a predetermined pressure. Thedeformable memory support 1 is designed to absorb the heightwisedispersion of all the micro-tips 6 securedly fixed to a substrate 7acting as support for the latter.

In the FIGURE, only two micro-tips 6 a and 6 b, securedly fixed to thesubstrate 7, are represented. Their height difference is exaggerated inthe FIGURE so as to clearly illustrate the operating principle of thedevice. Thus, whereas the micro-tip 6 b comes into contact with thememory support 1 without deforming the latter, the micro-tip 6 a, whichis longer, locally causes a small deformation of the memory support 1.The pressure exerted by the longer micro-tip is then insufficient tocause a deformation representative of a data to be recorded.

Data recording is subsequently performed, in conventional manner, byselective actuation of the micro-tips. Selective actuation of themicro-tips, designed for recording data, can be of thermal,electrostatic and/or mechanical type so as to form marks (correspondingfor example to changes of state, deformations, etc.) at preselectedmemory locations. In the case where recording selectively causes a localdeformation of the membrane, for example by pressure, the pressureexerted must then be substantially greater than the pressure exerted bythe micro-tips when the micro-tips of the array and the memory supportare brought into contact.

The deformations of the deformable memory layer 1 enabling thedispersion of the micro-tips to be absorbed when the micro-tip array andthe memory support are brought into contact are much smaller than themarks that may be caused, thermally, electrically or mechanically, whenrecording of the data is performed.

As represented in the FIGURE, the memory support 1 is preferably formedby a stack of thin layers comprising at least one deformable memorylayer deposited on a substrate 4.

The deformable memory layer can be formed by a flexible memory layer or,as represented in the FIGURE, by a stack of one memory layer 2 and oneflexible layer 3, the latter being deposited on the substrate 4. Aninterface layer 5 with the micro-tips 6 can cover the memory layer 2.When the micro-tip array and the memory support 1 are brought intocontact, a micro-tip 6 a pressing on the memory support 1 then resultsin a progressive deformation of the stack up to the flexible layer 3.This progressive deformation is a function of the hardness and thicknessof the different layers. The constitution and thickness of the differentlayers of the stack are adapted to the functionalities sought for and,in particular, to the recording mode chosen (thermal, electrical, etc.).

The flexible layer 3 can be formed by a polymer layer. For example, itcan be formed by photosensitive resin, in particular photoresist used inmicroelectronics in lift-off type removal processes. It can also beformed by a glue of controlled hardness or by a layer of PDMS typeelastomer silicon. The flexible layer 3 is preferably deposited on thesubstrate 4 by spin coating or by spray. Its thickness depends on theflexibility sought for and can for example be about a few micrometers oreven less if necessary.

The substrate 4 can be made from silicon or a possibly flexible plasticmaterial, for example polymethyl methacrylate (PMMA). In this case, itsflexibility can contribute to the flexibility of the stack forming thememory support 1 and its thickness can be reduced to less than onemillimeter.

The constitution of the memory layer 2 depends on the data recordingmethod chosen. This layer can notably be made from polymer or a phasechange material, either insulating or conducting. In all cases, thememory layer has to be as thin as possible to preserve the requiredflexibility of the memory support. It thus generally has a thickness ofless than one micrometer. It can for example be deposited by PVD, forexample by cathode sputtering, by PECVD or by spin coating on theflexible layer 3.

If the write process chosen is an electric write process, it may benecessary to make the flexible layer 3 conducting. This can inparticular be achieved by the choice of a conducting polymer material,by addition of an additive in the initially insulating material or byinterposing an additional conducting layer (not shown) between thememory layer 2 and the flexible layer 3. Such an additional conductinglayer can for example be a layer of carbon of a nature suitable forconduction and of small thickness (a few tens of nanometers).

The constitution of the interface layer 5 is designed to facilitateinteraction of the micro-tips 6 and of the memory support. For example,the interface layer 5 can be made from carbon, polymer, etc. Whateverits nature, it will have to be as thin as possible so as not to rigidifythe memory support 1.

1. A method for recording data by means of an array of micro-tipsarranged in a plane facing a memory support including a stack of thinlayers with at least one deformable memory layer, the method comprising:data recording by selective actuation of the micro-tips, the micro-tipsbeing fixed directly onto one and the same support substrate; bringingthe array of micro-tips and the memory support into contact with apredetermined pressure, which is insufficient to cause a deformationrepresentative of a data to be recorded, before the selective actuationof the micro-tips for data recording, said pressure enabling thedispersion of heights of the micro-tips of the array of micro-tips to beabsorbed by the deformable memory layer.
 2. The method according toclaim 1, wherein data recording is of electric type.
 3. The methodaccording to claim 1, wherein data recording is of thermal type.
 4. Arecording device for implementation of the method according to claim1,comprising: means for absorbing the dispersion of the heights of themicro-tips of the array; and means for recording by the selectiveactuation of the micro-tips, wherein the deformable memory layerconstitutes said means for absorbing when the memory support and thearray of micro-tips are brought into contact, at said predeterminedpressure, which is insufficient to cause a deformation representative ofa data to be recorded, the micro-tips, having an apex of nanometricdimension, being fixed directly onto one and the same support substrate.5. The device according to claim 4, wherein the memory layer isdeposited on a flexible layer deposited on the substrate.
 6. The deviceaccording to claim 5, wherein the flexible layer is made of polymer. 7.The device according to claim 6, wherein the flexible layer is made ofphotoresist.
 8. The device according to claim 5, wherein the flexiblelayer is a glue of controlled hardness.
 9. The device according to claim5, wherein the flexible layer is made of elastomer silicone.
 10. Thedevice according to claim 5, wherein the flexible layer has a thicknessof about a few micrometers.
 11. The device according to claim 5, whereinthe flexible layer is conducting.
 12. The device according to claim 5,further comprising: an additional conducting layer between the memorylayer and the flexible layer.
 13. The device according to claim 4,wherein the memory layer has a thickness of less than one micrometer.14. The device according to claim 4, further comprising: an interfacelayer with the micro-tips, covering the memory layer.
 15. The deviceaccording to claim 4, wherein the substrate is made of silicon.
 16. Thedevice according to claim 4, wherein the substrate is made of plasticmaterial with a thickness of less than one millimeter.